In a GPRS (General Packet Radio Services) system, a packet mode technique is used to transfer high-speed and low-speed data and signaling in an efficient manner. GPRS optimizes the use of network and radio resources. Applications based on standard data protocols are supported, and interworking is defined with IP-networks. GPRS is designed to support from intermittent and bursty data transfers through to occasional transmission of large volumes of data. Charging is typically based on the amount of data transferred.
GPRS introduces two new network nodes in the GSM mobile network. The Serving GPRS Support Node (SGSN) which is at the same hierarchical level as a mobile switching center (MSC) and which keeps track of the individual location of mobile stations (MS) and performs security functions and access control. The SGSN is connected to the base station system with a Frame Relay. The Gateway GSN (GGSN) provides interworking with external packet-switched networks, and is connected with SGSNs via an IP-based GPRS backbone network. A HLR (Home Location Register) of the GSM system is enhanced with GPRS subscriber information, and a VLR (Visitor Location Register) can be enhanced for more efficient coordination of GPRS and non-GPRS services and functionality, e.g. paging for circuit switched calls that can be performed more efficiently via the SGSN, and combined GPRS and non-GPRS location updates.
In order to access the GPRS services, an MS first makes its presence known to the network by performing a GPRS attach. This operation establishes a logical link between the MS and SGSN, and makes the MS available for paging via the SGSN, and notification of incoming GPRS data. In order to send and receive GPRS data, the MS shall activate the packet data address it wants to use. This operation makes the MS known in the corresponding GGSN and interworking with external data networks can commence. User data is transferred transparently between the MS and the external data networks with a method known as capsulating and tunneling, wherein data packets are equipped with GPRS-specific protocol information and transferred between the MS and the GGSN. This transparent transfer method lessens the requirement for the GPRS mobile network to interpret external data protocols, and it enables easy introduction of additional interworking protocols in the future.
In case a mobile subscriber wishes to access a value added service (VAS) provided by an IP network, a service specific charging is a mandatory feature of the corresponding VAS platform for mobile operators. This means that operators need service platforms which are capable of performing charging based on e.g. an accessed WML content or URL (Uniform Resource Locator) and delivered messages. However, MS identification in VAS platforms connected to the GPRS network or other mobile packet switched networks is not trivial. The reason therefore is that a VAS platform receives only IP packets from a certain source address which is normally only a dynamic IP address of an MS and thus not sufficient at all for identifying that MS.
Furthermore, an MSISDN (Mobile Station ISDN number) is required which is especially important for messaging services (e.g. multimedia messaging) in order to prevent additional HLR queries.
A known MS identification is performed e.g. by using user names, passwords or cryptographic keys. However, these types of solutions are complex to operate/manage for mobile operators. Moreover, such solutions normally require their own management systems and data bases which are not necessarily consistent with existing billing or charging systems of mobile operators where the IMSI (International Mobile Subscriber Identity) or the MSIDSN are the key of the CDRs (Call Detail Records).
Alternatively, an authentication service could be performed in the HLR. However, this solution leads to a significant rise of the load in the HLR which is already a crucial node.